1. Field of the Invention
This invention relates to a transistor read-only memory, and more particularly in such a memory, to a unique arrangement of the transistors making up the cells with the sensing transistors so as to obtain a very high storage density.
2. Background Art
Transistor read-only memories are well known in the art and widely used. Such a memory comprises orthogonal word lines and bit lines at the intersections of which memory cells are provided. Binary information of a first type, for instance a "1", is stored in a cell when said cell includes an active transistor, i.e. when the collector of said active transistor is connected to a biasing voltage supply, the base to the word line and the emitter to the bit line, while binary information of a second type, for instance a "0", is stored in a cell when said cell does not include any transistor or when the connections of the transistor to the various lines are not completed in the cell.
As background material for the present invention, reference may be made to French patent application 2 261 594, which relates to a programmable read-only memory including bipolar transistors which are connected or not through a fuse in the collector path, said memory being consistent with the well-known emitter coupled logic (ECL) circuits. Word line addressing is ensured by means of an addressing transistor the emitter of which is coupled with the emitters of the word line transistors. Additionally, reference may be made to French patent applications Nos. 2 300 395 and 2 300 397 which describe means allowing information to be written into a memory of the programmable type in which the emitters of the cell transistors are, or selectively are not, connected to the bit lines through resistors. Also French patent application No. 2 300 396 describes a memory of this type, including means to make the time required to access the information contained in the memory constant.
In the above-indicated patent applications, the information is sensed or detected by means of reading transistors the emitters of which are connected to the bit lines and which, therefore, make up current switches with the transistors of the selected memory cells. However, such applications are directed to improving the performance of read-only memory assemblies and not to improving density, i.e. storage capacity.
An object of this invention is to provide a very high density integrated read-only memory, requiring little power and of low cost.